A sounding reference signal (SRS) is a reference signal used to measure an uplink channel. A network device may measure an uplink channel based on an SRS sent by a terminal device, to obtain channel state information (CSI) of the uplink channel, to schedule an uplink resource.
In some cases, the terminal device needs to send an SRS in an antenna switching manner. For example, in some systems characterized by channel reciprocity, the network device may estimate CSI of a downlink channel by using the CSI of the uplink channel obtained by measuring the uplink channel, to schedule a downlink resource. However, if a quantity of uplink antennas configured for the terminal device is less than a quantity of downlink antennas, the terminal device needs to switch a plurality of antennas to send a plurality of SRSs, so that the network device obtains CSI of a plurality of downlink channels.
Currently, in a current method, the terminal device may calculate a to-be-switched antenna based on each transmit opportunity of a reference signal. However, this method is strongly correlated with a transmission period of the reference signal, and has a limitation to some extent. For example, in some systems such as a 5G new radio access technology (NR) system, because transmission of some SRSs is not periodic, the terminal device cannot determine a to-be-switched antenna based on a transmission period, and therefore cannot perform antenna switching.